System and method for mitigating electromagnetic interference when acquiring image data

ABSTRACT

A digital X-ray detector is provided. The digital X-ray detector includes control circuitry. The control circuitry is configured to obtain an electromagnetic interference (EMI) frequency of an EMI signal, to receive a signal to start a scan, to ensure EMI noise is in a same phase during acquisition of offset images and read images to enable a subtraction of the EMI noise, and to start the scan.

BACKGROUND

The subject matter disclosed herein relates generally to digital X-rayimaging systems and, more particularly, to techniques for mitigating theeffects of electromagnetic interference (EMI) during image acquisitionwith such systems.

A number of radiological and fluoroscopic imaging systems of variousdesigns are known and are presently in use. Such systems generally arebased upon generation of X-rays that are directed toward a subject ofinterest. The X-rays traverse the subject and impact a digital detectoror an image intensifier. In medical contexts, for example, such systemsmay be used to visualize internal bones, tissues, and organs, anddiagnose and treat patient ailments. In other contexts, parts, baggage,parcels, and other subjects may be imaged to assess their contents. Inaddition, radiological and fluoroscopic imaging systems may be used toidentify the structural integrity of objects and for other purposes.

Increasingly, such X-ray systems use digital circuitry, such assolid-state detectors, for detecting the X-rays, which are attenuated,scattered or absorbed by the intervening structures of the subject. Itwill be appreciated that raw image data acquired via such X-ray systemsmay include a number of artifacts or other undesirable elements thatmay, if left uncorrected, result in visual artifacts in a reconstructedimage based on the raw image data. In turn, these visual artifacts maynegatively impact the ability of a user or computer to discern finerdetails in the image. Some artifacts may be due to presence ofelectromagnetic interference (EMI) in the imaging environment. Sourcesof EMI may include, for example, various electrical and electroniccomponents that may be utilized in the vicinity of the X-ray imagingsystem. There is a need, therefore, for improved approaches to mitigatethe effects of EMI during image acquisition.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the originally claimedsubject matter are summarized below. These embodiments are not intendedto limit the scope of the claimed subject matter, but rather theseembodiments are intended only to provide a brief summary of possibleforms of the subject matter. Indeed, the subject matter may encompass avariety of forms that may be similar to or different from theembodiments set forth below.

In accordance with an embodiment, a digital X-ray detector is provided.The digital X-ray detector includes control circuitry. The controlcircuitry is configured to obtain an electromagnetic interference (EMI)frequency of an EMI signal, to receive a signal to start a scan, toensure EMI noise is in a same phase during acquisition of offset imagesand read images to enable a subtraction of the EMI noise, and to startthe scan.

In accordance with another embodiment, an X-ray imaging method isprovided. The method includes utilizing a digital X-ray detector toobtain an electromagnetic interference (EMI) frequency of an EMI signal,to receive a signal to start a scan, to ensure EMI noise is in a samephase during acquisition of offset images and read images to enable asubtraction of the EMI noise, and to start the scan.

In accordance with a further embodiment, an imaging system is provided.The imaging system includes an X-ray source and a digital X-raydetector. The imaging system also includes control circuitry configured,via the digital X-ray detector, to obtain an electromagneticinterference (EMI) frequency of an EMI signal, to receive a signal tostart a scan, to ensure EMI noise is in a same phase during acquisitionof offset images and read images to enable a subtraction of the EMInoise, and to start the scan.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the disclosedsubject matter will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical overview of a digital X-ray imaging system inwhich the present technique may be utilized;

FIG. 2 is a diagrammatical representation of the functional circuitry ina detector of the system of FIG. 1 to produce image data forreconstruction;

FIG. 3 is a block diagram of a processor-based device or system that maybe configured to implement functionality described herein in accordancewith one embodiment;

FIG. 4 is a diagrammatical representation of a portion of an acquisitionsequence in which both image data and offset data are acquired forcorrection of electromagnetic interference (EMI) artifacts;

FIG. 5 is a graphical representation of a low frequency magnetic fieldoverlaid on a detector signal;

FIG. 6 is a flow chart of an embodiment of a method for correcting EMIartifacts in image data;

FIG. 7 is a flow chart of an embodiment of a method for synchronizing animage acquisition sequence;

FIG. 8 is a flow chart of an embodiment of a method for determining afrequency of an EMI signal; and

FIG. 9 is a schematic diagram illustrating the effect of synchronizationof image acquisition to an EMI signal on row correlated noise.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, all features ofan actual implementation may not be described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present subjectmatter, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Furthermore, any numerical examples in the following discussion areintended to be non-limiting, and thus additional numerical values,ranges, and percentages are within the scope of the disclosedembodiments.

The present disclosure provides for methods and systems to synchronizeX-ray image acquisition sequences for radiographic detectors where timedependent noise (e.g., row correlated noise which occurs in a directionof the sampling) is present due to electromagnetic interference (EMI)such as low frequency EMI (e.g., 60 Hertz (Hz) or less). The techniquesdiscussed below may synchronize the scans of the detector to occur at aparticular time period that is a multiple of a period of the EMI signal.The scans may include a read or readout (where the detector panel isscanned and detector data such as X-ray image data is acquired) or ascrub (where the detector panel is scanned to reset the detectorcircuitry but no data is read). In certain embodiments, the EMIfrequency may be determined from offset data or dark images (i.e.,detector data collected in the absence of radiation). The offset datamay be utilized to correct the X-ray image data to generate correctedX-ray images where EMI artifacts are minimized due to the cancellationof the time dependent noise. The EMI mitigation techniques may beutilized across all orientations (X-, Y-, and Z-axes). The techniquesdescribed below may be utilized in a variety of radiographic imagingsystems, such as computed tomography (CT) systems, fluoroscopic imagingsystems, mammography systems, tomosynthesis imaging systems,conventional radiographic imaging systems, and so forth. However, itshould be appreciated that the described techniques may also be used innon-medical contexts (such as security and screening systems andnon-destructive detection systems).

Turning now to the drawings, FIG. 1 illustrates diagrammatically animaging system 10 for acquiring and processing discrete pixel imagedata. In the illustrated embodiment, system 10 is a digital X-ray systemdesigned both to acquire original image data and to process the imagedata for display in accordance with the present technique. The imagingsystem 10 may be a stationary system disposed in a fixed X-ray imagingroom or a mobile X-ray system. In the embodiment illustrated in FIG. 1,imaging system 10 includes a source of X-ray radiation 12 positionedadjacent to a collimator 14. Collimator 14 permits a stream of radiation16 to pass into a region in which a subject, such as a human patient 18is positioned. A portion of the radiation 20 passes through or aroundthe subject and impacts a digital X-ray detector, represented generallyat reference numeral 22. The detector 22 may be portable or permanentlymounted to the system 10. In certain embodiments, the detector 22 mayconvert the X-ray photons incident on its surface to lower energyphotons, and subsequently to electric signals, which are acquired andprocessed to reconstruct an image of the features within the subject. Inother embodiments, such as in a direct conversion implementation, theincident radiation itself may be measured without an intermediaryconversion process.

Source 12 is controlled by a power supply/control circuit 24 whichfurnishes both power and control signals for examination sequences.Moreover, detector 22 is coupled to a detector controller 26 whichcommands acquisition of the signals generated in the detector 22.Detector controller 26 may also execute various signal processing andfiltration functions, such as for initial adjustment of dynamic ranges,interleaving of digital image data, and so forth. Both powersupply/control circuit 24 and detector controller 26 are responsive tosignals from a system controller 28. In general, system controller 28commands operation of the imaging system to execute examinationprotocols and to process acquired image data. In the present context,system controller 28 also includes signal processing circuitry,typically based upon a general purpose or application-specific digitalcomputer; and associated manufactures, such as optical memory devices,magnetic memory devices, or solid-state memory devices, for storingprograms and routines executed by a processor of the computer to carryout various functionalities (e.g., offset correction to remove EMIgenerate artifacts), as well as for storing configuration parameters andimage data; interface protocols; and so forth. In one embodiment, ageneral or special purpose computer system may be provided withhardware, circuitry, firmware, and/or software for performing thefunctions attributed to one or more of the power supply/control circuit24, the detector controller 26, and/or the system controller 28 asdiscussed herein.

In the embodiment illustrated in FIG. 1, system controller 28 is linkedto at least one output device, such as a display or printer as indicatedat reference numeral 30. The output device may include standard orspecial purpose computer monitors and associated processing circuitry.One or more operator workstations 32 may be further linked in the systemfor outputting system parameters, requesting examinations, viewingimages, and so forth. In general, displays, printers, workstations, andsimilar devices supplied within the system may be local to the dataacquisition components, or may be remote from these components, such aselsewhere within an institution or hospital, or in an entirely differentlocation, linked to the image acquisition system via one or moreconfigurable networks, such as the Internet, virtual private networks,and so forth.

FIG. 2 is a diagrammatical representation of functional components ofdigital detector 22. FIG. 2 also represents an imaging detectorcontroller or IDC 34 which will typically be configured within detectorcontroller 26. IDC 34 includes a CPU or digital signal processor, aswell as memory circuits for commanding acquisition of sensed signalsfrom the detector. In one implementation, IDC 34 is coupled via two-wayfiberoptic conductors to detector control circuitry 36 within detector22. In certain presently contemplated embodiments, other communicationssystems and technologies may be used, such as Ethernet communicationsprotocols, and wireless communications devices and protocols. IDC 34thereby exchanges command signals for image data within the detectorduring operation.

Detector control circuitry 36 receives DC power from a power source,represented generally at reference numeral 38. Detector controlcircuitry 36 is configured to originate timing and control commands forrow and column electronics used to acquire image data during dataacquisition phases of operation of the system. Circuitry 36 thereforetransmits power and control signals to reference/regulator circuitry 40,and receives digital image pixel data from circuitry 40.

In a present embodiment, detector 22 consists of a scintillator thatconverts X-ray photons received on the detector surface duringexaminations to lower energy (light) photons. An array of photodetectorsthen converts the light photons to electrical signals which arerepresentative of the number of photons or the intensity of radiationimpacting individual pixel regions of the detector surface. In certainpresently contemplated embodiments, the X-ray photons may be directlyconverted to electrical signals. Readout electronics convert theresulting analog signals to digital values that can be processed,stored, and displayed, such as in a display 30 or a workstation 32following reconstruction of the image. In a present form, the array ofphotodetectors is formed of amorphous silicon. The array elements areorganized in rows and columns, with each element consisting of aphotodiode and a thin film transistor. The cathode of each diode isconnected to the source of the transistor, and the anodes of all diodesare connected to a negative bias voltage. The gates of the transistorsin each row are connected together and the row electrodes are connectedto the scanning electronics as described below. The drains of thetransistors in a column are connected together and the electrode of eachcolumn is connected to an individual data channel of the readoutelectronics.

In the particular embodiment illustrated in FIG. 2, by way of example, arow bus 42 includes a plurality of conductors for enabling readout fromvarious rows of the detector 22, as well as for disabling rows andapplying a charge compensation voltage to selected rows, where desired.A column bus 44 includes additional conductors for commanding readoutfrom the columns while the rows are sequentially enabled. Row bus 42 iscoupled to a series of row drivers 46, each of which commands enablingof a series of rows in the detector. Similarly, readout electronics 48are coupled to column bus 44 for commanding readout of all columns ofthe detector.

In the illustrated embodiment, row drivers 46 and readout electronics 48are coupled to a detector panel 50, which may be subdivided into aplurality of sections 52. Each section 52 is coupled to one of the rowdrivers 46, and includes a number of rows. Similarly, each column driver48 is coupled to a series of columns. The photodiode and transistorarrangement mentioned above thereby define a series of pixels ordiscrete picture elements 54 which are arranged in rows 56 and columns58. The rows and columns define an image matrix 60, having a height 62and a width 64.

As also illustrated in FIG. 2, each pixel 54 is generally defined at arow and column crossing, at which a column electrode (or data line) 68crosses a row electrode (or scan line) 70. As mentioned above, a thinfilm transistor 72 is provided at each crossing location for each pixel,as is a photodiode 74. As each row is enabled by row drivers 46, signalsfrom each photodiode 74 may be accessed via readout electronics 48, andconverted to digital signals for subsequent processing and imagereconstruction. Thus, an entire row of pixels in the array is controlledsimultaneously when the scan line 70 attached to the gates of all thetransistors of pixels on that row is activated. Consequently, each ofthe pixels in that particular row is connected to a data line 68,through a switch, which is used by the readout electronics to restorethe charge to the photodiode 74 and measure an amount of chargedepletion resulting from irradiation.

It should be noted that in certain systems, as the charge is restored toall the pixels in a row simultaneously by each of the associateddedicated readout channels, the readout electronics is converting themeasurements from the previous row from an analog voltage to a digitalvalue. Furthermore, the readout electronics may transfer the digitalvalues from rows previous to the acquisition subsystem, which willperform some processing prior to displaying a diagnostic image on amonitor or writing it to film. In at least some embodiments, the digitaldetector 22 may include data processing circuitry 66 configured toperform some local processing of the data acquired via the detectorpanel 50 within the digital detector itself. For instance, as discussedin greater detail below, the digital detector 22 may be configured toperform synchronization of scans (e.g., scrub and/or read) as a multipleof a period of an EMI signal and offset correction (e.g., to reduce EMIgenerated noise such as row correlated noise) to the acquired dataindependent of a host processing system, such as the system controller28. Additionally, in one embodiment, the digital detector 22 apply suchcorrection to the acquired data before outputting the data to othercomponents of the system 10.

The circuitry used to enable the rows may be referred to in a presentcontext as row enable or field effect transistor (FET) circuitry basedupon the use of field effect transistors for such enablement (rowdriving). The FETs associated with the row enable circuitry describedabove are placed in an “on” or conducting state for enabling the rows,and are turned “off” or placed in a non-conducting state when the rowsare not enabled for readout. Despite such language, it should be notedthat the particular circuit components used for the row drivers andcolumn readout electronics may vary, and the present invention is notlimited to the use of FETs or any particular circuit components.

Various functionality, including image data correction described herein,may be performed by, or in conjunction with, a processor-based system76, which is generally depicted in FIG. 3 in accordance with oneembodiment. For example, the various controllers and circuitry discussedherein may include, or be partially or entirely embodied in, aprocessor-based system, such as that presently illustrated. Theprocessor-based system 76 may be a general-purpose computer, such as apersonal computer, configured to run a variety of software, includingsoftware implementing all or part of the functionality described herein.Alternatively, in other embodiments, the processor-based system 76 mayinclude, among other things, a distributed computing system, or anapplication-specific computer or workstation configured to implement allor part of the presently described functionality based on specializedsoftware and/or hardware provided as part of the system. Further, theprocessor-based system 76 may include either a single processor or aplurality of processors to facilitate implementation of the presentlydisclosed functionality.

In one embodiment, the exemplary processor-based system 76 includes amicrocontroller or microprocessor 78, such as a central processing unit(CPU), which executes various routines and processing functions of thesystem 76. For example, the microprocessor 78 may execute variousoperating system instructions, as well as software routines configuredto effect certain processes, stored in or provided by a manufactureincluding one or more computer readable-media (at least collectivelystoring the software routines), such as a memory 80 (e.g., a randomaccess memory (RAM) of a personal computer) or one or more mass storagedevices 82 (e.g., an internal or external hard drive, a solid-statestorage device, or another storage device). In addition, themicroprocessor 78 processes data provided as inputs for various routinesor software programs, such as data provided as part of the presentsubject matter described herein in computer-based implementations.

Such data may be stored in, or provided by, the memory 80 or massstorage device 82. Alternatively, such data may be provided to themicroprocessor 78 via one or more input devices 84. The input devices 84may include manual input devices, such as a keyboard, a mouse, or thelike. In addition, the input devices 84 may include a network device,such as a wired or wireless Ethernet card, a wireless network adapter,or any of various ports or devices configured to facilitatecommunication with other devices via any suitable communicationsnetwork, such as a local area network or the Internet. Through such anetwork device, the system 76 may exchange data and communicate withother networked electronic systems, whether proximate to or remote fromthe system 76.

Results generated by the microprocessor 78, such as the results obtainedby processing data in accordance with one or more stored routines, maybe provided to an operator via one or more output devices, such as adisplay 86 and/or a printer 88. Based on the displayed or printedoutput, an operator may request additional or alternative processing orprovide additional or alternative data, such as via the input device 84.Communication between the various components of the processor-basedsystem 76 may typically be accomplished via a chipset and one or morebusses or interconnects which electrically connect the components of thesystem 76. In one embodiment, the exemplary processor-based system 76can be configured to, among other things, receive image data, receiveoffset data, apply offset correction to the image data via the offsetdata, and output the corrected image data.

FIG. 4 represents an image data acquisition protocol timeline designedto permit the correction of image data for EMI artifacts in accordancewith the techniques discussed below. The timeline, designated generallyby reference numeral 90 may include periods of the detector performingvarious scans for scrubbing and data readout operations. As will beappreciated by those skilled in the art, to account for inevitable lossof charge of the photodiodes of the detector, it may be useful torecharge the photodiodes periodically by a scrubbing operation asindicated by frame 94 prior to activation of the X-ray source and frame95 subsequent to activation of the X-ray source. Essentially, suchoperations stabilize the FET threshold voltage but do not readout data.Prior to the X-ray source being activated, readout (as indicated byframe 94) of the detector enables the acquisition of offset images ordark images (i.e., images acquired when the detector is not exposed toradiation from the source). As depicted, only a single readout isdepicted prior to activation of the X-ray source. In certainembodiments, a plurality of offset images (e.g., 2, 3, 4, etc.) may beacquired prior to activation of the X-ray source. The offset data thatis read out may also be similarly affected by the EMI, when such EMI ispresent. As described in greater detail below, a respective frequency(e.g., 50 Hz, 60 Hz, etc.) of one or more EMI signals may be determinedfrom one or more offset images. At some point in the data acquisitionprotocol, the X-ray source will be activated (e.g., as indicated byarrow 96) such that the detector is impacted by X-ray radiation during areception period. The X-ray radiation will cause depletion in the chargeof the photodetectors at each pixel location corresponding to the amountof X-ray radiation received at the location on the scintillator. TheX-ray reception period is followed by one or more data readouts asindicated by frames 98. These readouts 98, may also include readout ofX-ray image data that is affected by EMI, when EMI is present at thesystem. As described in greater detail below, the frequency of the EMImay be utilized in synchronizing the scans (e.g., X-ray image scans 98,scrubs 92) that occur subsequent to the activation of the X-ray source.In particular, these scans may be synchronized to a master clock in thedetector hardware (e.g., FPGA) so that each scan is started at amultiple of a period (i.e., amount of time to complete a single cycle)of the EMI signal. In certain embodiments, when multiple low frequency(e.g. 60 Hz or less) EMI signals are present, the scans may besynchronized so that each scan is started at a multiple of the eachrespective period of the multiple EMI signals. Row correlated noise(e.g., due to the EMI) is minimized when a total time 100 from the endof one scan or frame to the end of the next scan or frame time issynchronized with the frequency of the EMI. The total time 100 equalsthe frame time 102 (e.g., duration of scan) and a time between frames(TBF) or scans 104. The one or more offset images acquired above may beutilized in correcting X-ray image data during the synchronized scans toremove EMI artifacts.

FIG. 5 is a graphical representation 106 (e.g., from an oscilloscope) ofa low frequency magnetic field overlaid on a detector signal. The graph106 includes an X-axis 108 representing time and a Y-axis 110representing voltage. As depicted, a signal 112 of low frequencymagnetic field (e.g., 60 Hz) is overlaid on a detector signal 114. Thedetector signal 114 includes scrub (S) and readout (R) periods. Asdepicted, the magnetic field signature goes through numerous periods116, a scrub or readout period. As described in greater detail below,synchronization of the scrubs (i.e., scrubs and/or readouts) to amultiple of the period of the signal 112 may be utilized to minimize EMIartifacts in the generated X-ray images.

FIG. 6 is a flow chart of an embodiment of a method 118 for correctingEMI artifacts in image data. One or more of the steps may be performedby control/processing circuitry of the digital X-ray detector 22,another component of the imaging system 10 (e.g., system controller 28),or a remote processing device. The method 118 includes, prior toacquiring offset or dark images, synchronizing the offset scans with theone or more low frequency EMI signals (block 119). The method 118includes acquiring one or more offset or dark images (i.e., detectordata collected in the absence of radiation) (block 120). As described ingreater detail below, the offset images may be utilized in determining arespective frequency of one or more low frequency EMI signals. Themethod 118 also includes synchronizing scans (e.g., scrubs and/orreadouts) with the one or more EMI signals (block 122) once the X-rayimage acquisition begins. The method 118 further includes starting theX-ray exposure (block 124). Subsequent to the beginning of the X-rayexposure, the method 118 includes acquiring X-ray image data, via thedetector 22, during a synchronized image acquisition sequence (block126). The method 118 further includes correcting the X-ray image datawith the one or more acquired offset images to generate reconstructedimages corrected for EMI artifacts. For example, each pixel of the imagedata may have the respective offset data for that pixel subtracted fromit. In certain embodiments, the offset data utilized for correction maybe from a single scan or an average of multiple scans (e.g., 4 offsetscans). The synchronization of the image acquisition sequence enablesthe time dependent noise to be canceled out, thus, minimizing the rowcorrelated noise.

FIG. 7 is a flow chart of an embodiment of a method 130 forsynchronizing an image acquisition sequence (e.g., block 122 of themethod 118). The method 130 may be performed by control/processingcircuitry of the digital X-ray detector 22. In certain embodiments, themethod 130 includes calculating an EMI frequency from offset dataacquired prior to the X-ray exposure (block 132). In certainembodiments, more than one EMI frequency may be calculated in thepresence of multiple low frequency EMI signals. Calculating the EMIfrequency enables the detector 22 to perform auto-detection to determinethe presence of low frequency EMI signals (e.g., 60 Hz or lower). Sincethe typical read time for a scan ranges from 100 to 300 milliseconds(ms), the low frequency EMI signals may be extracted via image analysistechniques (such as fast Fourier transformation (FFT) as describedbelow). In certain embodiments, in the absence of an auto-detection, thefrequency utilized for synchronization may default to a typical powerline frequency (e.g., 50 Hz, 60 Hz, or a combination) while ignoringother low frequency EMI sources not linked to power lines (block 134).In certain embodiments, the method 130 includes receiving an input(e.g., user input) of the EMI frequency (block 136).

The method 130 includes receiving a signal (e.g., from control circuit24 or system controller 28) to start the scan (e.g., readout or scrub)(block 138). The method 130 also includes adding a delay to the start ofa scan time (e.g., the TBF or synchronization period), which is amultiple of the period of the EMI signal (block 140). For example, a 50Hz EMI field has a period of 20 ms and a 60 Hz EMI field has a period of16.666 ms. The TBF or synchronization period may be a multiple of 2, 3,4, 5, or any other multiple of the period of the EMI signal. Forexample, the TBF or synchronization period may be 40 ms, 60 ms, 80 ms,100 ms, or another period when associated with the 50 Hz EMI field. TheTBF or synchronization period may be 33.333 ms, 49.999 ms, 66.666 ms,83.333 ms, or another period when associated with the 60 Hz EMI field.In certain embodiments, the scans may be synchronized to multiple EMIfrequencies (e.g., both 50 Hz and 60 Hz) at the same time. For example,the TBF or synchronization period to cancel out the 50 Hz and 60 Hzfields may be a multiple of the period of both frequencies such as 100ms period (which is a multiple of 5 relative the period the 50 Hz fieldand a multiple of 6 to the 60 HZ field). The method 130 further includesstarting the scan (e.g., readout) after the synchronization period(block 142).

FIG. 8 is a flow chart of an embodiment of a method 144 for determininga frequency of an EMI signal or field (e.g., block 132 of the method130). The method 144 may be performed by control/processing circuitry ofthe digital X-ray detector 22. It should be noted that the method 144 isa single example of an image analysis technique that may be utilized toextract the low frequency field from the offset image data. In addition,the method 144 may be utilized to determine the frequencies of multipleEMI signals or fields that are present. The method 144 includesacquiring one or more offset or dark images (i.e., detector datacollected in the absence of radiation) (block 146). The method 144 alsoincludes extracting a one or more data lines (from one or more columns)for all scans lines (i.e., rows) from a single offset scan or an averageof multiple offset scans (block 148). The method 144 further includesperforming FFT on a signal representative of the extracted data togenerate a discrete Fourier transforms (DFTs) at different frequencies(block 150). The method 144 includes limiting the frequency of the DFTsto within a low frequency range defined by a lower frequency (f1) and ahigher frequency (f2) so that frequency of the DFT is between f1 and f2(block 152). In certain embodiments, the low frequency range may bedefined by the frequency of a power line (e.g., 50 Hz, 60 Hz, etc.). Thelow frequency range may be plus or minus a percentage of the power linefrequency (e.g., ±2 percent, ±3 percent etc.). For example, plus orminus 3 percent of 50 Hz would set f1 as 48.5 Hz and f2 as 51.5 Hz andplus or minus 3 percent of 60 Hz would set f1 as 58.2 Hz and f2 as 61.8Hz.

In certain embodiments, the method 144 includes defining a thresholdlimit for comparison to the DFT frequency (block 154). In certainembodiments, the threshold limit may be determined experimentally. Themethod 144 may include comparing the DFT frequency to the thresholdlimit (block 156) to determine if the DFT frequency is greater than thethreshold limit (block 158). If the DFT frequency is greater than thethreshold limit, then the method 144 includes setting the DFT frequencyas the EMI frequency (block 160). If the DFT frequency is not greaterthan the threshold limit, then the method 144 includes setting the EMIfrequency as zero or null (block 162) and, thus, determining there is noEMI field.

In certain embodiments, after limiting the frequency range for the DFTs(block 152, the method 144 includes comparing the DFT frequency to oneor more specific EMI frequencies (e.g., 50 Hz, 60 Hz, etc.) (block 164)to determine if the DFT frequency equals one of the specific EMIfrequencies (block 166). If the DFT frequency equals a specific EMIfrequency, the method 144 includes setting the DFT frequency as the EMIfrequency (block 160). If the DFT frequency does not equal a specificEMI frequency, the method includes setting the EMI frequency as zero ornull (block 162) and, thus, determining there is no EMI field.

FIG. 9 is a schematic diagram illustrating the effect of synchronizationof image acquisition to an EMI signal on row correlated noise. FIG. 9depicts two graph 168, 170. Each graph 168, 170 includes an X-axis 172representing TBF in microseconds and a Y-axis 174 representing noiseamplitude. The EMI signal is 60 Hz. Row correlated noise signal plotsfor two different imaging modes in response to the 60 HZ EMI signal arerepresented by plots 176 (solid), 178 (dashed), respectively. Graph 168illustrates the row correlated noise relative to the TBF in the absenceof synchronization of the scan (e.g., readout or scrub) to the period ofthe EMI signal. As depicted in graph 168, the row correlated noisevaries with the TBF. In addition, as depicted in graph 168, the rowcorrelated noise minimum is periodic. Graph 170 illustrates the rowcorrelated noise relative to the TBF after synchronization of the scanto the period of the EMI signal. As depicted in graph 170, the rowcorrelated noise is consistently at a minimum.

Technical effects of the disclosed embodiments include providing methodsand systems to synchronize X-ray image acquisition sequences forradiographic detectors to minimize time dependent noise (e.g., rowcorrelated noise) due to low frequency EMI (e.g., 60 Hz or less). Thetechniques discussed below may synchronize the scans (e.g., readout orscrub) of the detector to occur at a particular time period that is amultiple of a period of the EMI signal. In certain embodiments, the EMIfrequency may be determined from offset data or dark images. The offsetdata may be utilized to correct the X-ray image data to generatecorrected X-ray images where EMI artifacts are minimized due to thecancellation of the time dependent noise. The EMI mitigation techniquesmay be utilized across all orientations (X-, Y-, and Z-axes). Thedisclosed techniques may improve image quality in the presence of an EMIfield as well as provide low frequency EMI immunity.

This written description uses examples to disclose the present subjectmatter, including the best mode, and also to enable any person skilledin the art to practice the present approaches, including making andusing any devices or systems and performing any incorporated methods.The patentable scope is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims.

The invention claimed is:
 1. A digital X-ray detector, comprising:control circuitry configured to: obtain an electromagnetic interference(EMI) frequency of an EMI signal; receive a signal to start a scan;ensure EMI noise is in a same phase during acquisition of offset imagesand read images to enable a subtraction of the EMI noise; and start thescan; wherein the control circuitry is configured to obtain a respectiveEMI frequency of a plurality of EMI signals and to synchronize the scanbased on the respective EMI frequencies so that a time of start for thescan is a multiple of each respective period of the plurality of EMIsignals.
 2. The digital X-ray detector of claim 1, wherein the scancomprises a scrub to reset detector circuitry or a read to acquire X-rayimage data.
 3. The digital X-ray detector of claim 1, wherein controlcircuitry is configured to obtain the EMI frequency via receiving a userinput of the EMI frequency.
 4. The digital X-ray detector of claim 1,wherein the control circuitry is configured to obtain the EMI frequencyby calculating the EMI frequency from one or more offset scans acquiredby the digital X-ray detector.
 5. The digital X-ray detector of claim 4,wherein the control circuitry is configured to calculate the EMIfrequency by extracting data from the one or more offset scans,performing fast Fourier transformation on a signal representative of thedata, and determine if a frequency of a discrete Fourier transform (DFT)of the signal within a predetermined frequency range is greater than adefined frequency threshold.
 6. The digital X-ray detector of claim 5,wherein the control circuitry is configured to set the EMI frequency asthe frequency of the DFT when the frequency of the DFT is greater thanthe defined frequency threshold and to set the EMI frequency as zerowhen the frequency of the DFT is not greater than the defined frequencythreshold.
 7. The digital X-ray detector of claim 4, wherein the controlcircuitry is configured to calculate the EMI frequency by extractingdata from the one or more offset scans, performing fast Fouriertransformation on a signal representative of the data, and determine ifa frequency of the discrete Fourier transform (DFT) of the signal equalsa specific EMI frequency.
 8. The digital X-ray detector of claim 7,wherein the control circuitry is configured to set the EMI frequency asthe frequency of the DFT when the frequency of the DFT equals thespecific EMI frequency and to set the EMI frequency as zero when thefrequency of the DFT does not equal the specific EMI frequency.
 9. AnX-ray imaging method, comprising: utilizing a digital X-ray detector to:obtain an electromagnetic interference (EMI) frequency of an EMI signal,wherein obtaining the EMI frequency of the EMI signal comprisesreceiving a user input of the EMI frequency; receive a signal to start ascan; ensure EMI noise is in a same phase during acquisition of offsetimages and read images to enable a subtraction of the EMI noise; andstart the scan.
 10. The method of claim 9, wherein the scan comprises ascrub to reset detector circuitry or a read to acquire X-ray image data.11. The method of claim 9, wherein ensuring the EMI noise is in the samephase during acquisition of the offset images and the read imagescomprises synchronizing the scan based on the EMI frequency so that atime of start for the scan is a multiple of a period of the EMI signal.12. The method of claim 9, wherein obtaining the EMI frequency of theEMI signal comprises calculating the EMI frequency from one or moreoffset scans acquired by the digital X-ray detector.
 13. The method ofclaim 12, comprising: acquiring, via the digital X-ray detector, X-rayimage data with the scan; and performing offset correction on theacquired X-ray image data with the one or more offset scans to removeany EMI related artifacts to generate a corrected X-ray image.
 14. Animaging system comprising: an X-ray source; a digital X-ray detector;and control circuitry configured, via the digital X-ray detector, toobtain an electromagnetic interference (EMI) frequency of an EMI signal,to receive a signal to start a scan, to ensure EMI noise is in a samephase during acquisition of offset images and read images to enable asubtraction of the EMI noise, and to start the scan; wherein the controlcircuitry is configured, via the digital X-ray detector, to obtain arespective EMI frequency of a plurality of EMI signals and tosynchronize the scan based on the respective EMI frequencies so that atime of start for the scan is a multiple of each respective period ofthe plurality of EMI signals.
 15. The imaging system of claim 14,wherein the control circuitry is configured, via the digital X-raydetector, to obtain the EMI frequency by calculating the EMI frequencyfrom one or more offset scans acquired by the digital X-ray detector.16. The imaging system of claim 14, wherein the imaging system comprisesprocessing circuitry, and the processing circuitry is configured toperform offset correction on acquired X-ray image data with the one ormore offset scans to remove any EMI related artifacts to generate acorrected X-ray image.